In the production of hydrocarbons, such as crude oil and bitumen from a subterranean reservior, the characteristic of the formation has a substantial affect on the efficiency of production. It is expected that in the course of most production operations, the flowing hydrocarbon will carry with it an amount of the substrate from which it is being lifted. This effect is particularly noticeable in the instance of sandy formations which are subjected to thermal stimulation.
In the instance of a substrate comprised largely of unconsolidated sand particles, the flowing hydrocarbon will tend to carry excessive amounts of sand with it. Sand thus entering the well casing or liner, forms a substantial part of the flow and has detrimental effects on the overall operation, as well as on the equipment. For example, the size of the sand particles could be such that there is a propensity for it to block or at least partially plug holes and passages through which the flow passes. Further, the abrasive nature of the sand results in the wearing away or damage to parts which make up the well completion.
Operationally, the combined sand and hydrocarbon flow have to be treated and separated after being produced. The equipment needed for such separation generally constitutes a major and costly part of the production facility in which sand is a prevalent factor.
It can be appreciated that in the instance of bitumen production, and the production of viscous crude oil from a sandy environment, the problem of sand control will pose a major consideration. In the specific instance of bitumen, the normal thermal stimulation of a substrate through the use of hot fluids such as steam, will tend to promote the flow of sand. As the bitumen or viscous crude is released, it will carry along with it varying sized sand particles in its flow to the production string.
It has been found that where the hydrocarbon holding reservoir constitutes a relatively thin layer, there are advantages in the use of horizontal wells. The latter extend coextensively with the productive layer and can be more economical than a series of vertical wells, which pass through the layer at spaced apart points.
In the instance of a horizontal well, similarly to a vertical well, a pressurized hot medium is used to stimulate the substrate adjacent to the well. Thereafter the viscous hydrocarbon is caused to flow and gravitate toward the single well, and be produced as a hot, flowing stream.
In the instance of horizontal wells which are formed into tar sands, the problem of excessive sand production is particularly acute. As above noted, the hot bitumen is stimulated and caused to assume a fluid state, thereby carrying with it substantial quantities of sand which will enter the wall perforations in the horizontally positioned liner. These sand particles will tend to narrow such passages to a minimum opening, or completely obviate flow therethrough.
Efforts have been made through the use of replaceable screens, to minimize this flow of sand into a horizontal producing well. However, the very nature of the well, because it entends horizontally rather than veritcally, introduces problems not heretofore contemplated with respect to the in-situ formation of a suitable gravel pack. Since a gravel pack is among the most prevalent ways of minimizing sand production in vertical wells, such packs are considered to be of comparable efficiency if they can be adapted to be utilized in conjunction with a horizontal well.
The state of the art relative to in-situ gravel packing of hydrocarbon producing wells covers a broad spectrum of apparatus and methods. Essentially, however, the art is concerned primarily with packing of vertical and/or deviated wells, with open or closed casing, in which the gravel injection can be achieved by a gravity flow.
Examples of this type of gravel packs are disclosed in U.S. Pat. Nos. 4,066,127 and 4,124,074. In the shown patents, the gravel is introduced through the well and carried into a preformed vertical well cavity whereby to constitute the required sand barrier. This introduction of the gravel is achieved either by feeding the gravel alone, or in the form of a slurry.
In U.S. Pat. No. 2,434,239, the patentee extends the gravel pack concept into a portion of a deviated or sloping well, and even into a portion of a horizontal well. However the gravel as shown, particularly in the patentee's FIG. 3, is introduced to fill the entire borehole. This is achieved by progressively withdrawing the gravel carrying conduit as the borehole fills. The patentee's disclosure lacks the means for providing a gravel pack which surrounds the well liner and forms the necessary peripheral barrier to sand.
U.S. Pat. No. 3,261,401 is concerned at least in part with a gravel pack within a horizontal well. The pack in this instance, and as shown in FIGS. 4 and 5, is an integral part of the well liner, and is not installed in-situ.
Toward overcoming the foregoing problems, and for providing an in-situ gravel pack, the disclosed well completion is one that is commenced by first forming an elongated bore. The latter extends substantially horizontally whereby to lie longitudinally through a productive layer.
A perforated well liner or casing having a diameter substantially less than the diameter of the wellbore, is supportably positioned in the bore in a manner to define an annular passage. Said passage between the liner wall and the adjacent wall of the bore, is then furnished with a gravel pack. The pack is comprised of an unconsolidated mass of gravel sizes and grades which have been predetermined for the particular formation composition, to best form a barrier to migrating sand particles which would otherwise enter the liner.
The gravel pack annular cavity or longitudinal passage is formed by positioning the liner initially in the wellbore prior to introducing a gravel carrying slurry to said longitudial passage. Thereafter, the pack is completed by introduction of the gravel slurry about the liner sides as a slurry carrying conduit is progressively withdrawn from the well.
It is therefore an object of the invention to provide a gravel pack and method for use thereof in a substrate comprising a sandy composition and into which at least one horizontal producing well has been formed.
A further object is to provide a method for forming a gravel pack in situ about a horizontally extending well.
A still further object is to provide a gravel pack and method for applying the same about a well liner that is positioned in a horizontally extending wellbore.